Newark Mayor Cory Booker — the only star-studded contender who could potentially clear the field — has said publicly and told Democrats privately he’s not running for governor

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While national Republicans dream about a future Chris Christie presidency, Democrats are quietly pondering who can make him a one-term governor next year.

The only problem: There’s no standout Democrat stepping forward to take on the New Jersey governor — assuming he decides to run again, which isn’t a given. Newark Mayor Cory Booker — the only star-studded contender who could potentially clear the field — has said publicly and told Democrats privately he’s not running for governor.

The early void means this will be the first time in the state since 1996 the party out of power heads into the fall without a presumed front-runner.

On one level a challenge to Christie — who’s been picked to give the keynote speech at the Republican National Convention next month, several news outlets reported this week — would seem to be enticing to top-flight Democrats given the state’s leftward tilt. Democrats enjoy a 12-point registration advantage, though nearly half the electorate — 47 percent — is unaffiliated with a party.

But Christie, of course, is no ordinary Republican. The blunt former prosecutor is an inimitable national GOP star who last month eclipsed a 50 percent approval rating and will bring a national fundraising network to bear if he decides to pursue a second term. His in-your-face style may be wearing thin on some, but taking him out is another matter.

And that makes the calculus considerably trickier for Democrats.

Booker is seen as keeping his powder dry for a shot at a U.S. Senate seat. One top ranking Garden State Democrat told POLITICO Booker was candid about why he’s not running for governor.

“I don’t think Christie can be beaten,” the mayor said in a private conversation earlier this year, according to the Democrat.

Booker political adviser Mark Matzen didn’t dispute the account — “I don’t know whether he said it or not” — but attempted to crack the door back open for his client, insisting a bid for governor hasn’t been ruled out.

“When the mayor says he’s not running, he usually says I’m not running for governor now, as in right now. We are definitely keeping our options open, not committing one way or the other to anybody. He’s being pushed by a lot of folks to run,” said Matzen.

Nevertheless, it’s Matzen’s job to keep Booker’s options open. Outside observers, citing the mayor’s amicable relationship with the governor, still believe the odds are stacked against a Booker run.

Unless Christie decides to forgo a second term.

That possibility, however slim, is a crucial part of Democrats’ calculation as they sketch out a strategy for 2013. The campaign will begin to take shape in early September at the Democratic National Convention, when the most serious candidates fly to Charlotte to schmooze with deep-pocketed donors and activists.

“I think it’s an open question whether Gov. Christie runs for reelection. Arguably he’s already built a good narrative that’s unlikely to get better in a second term. And he’s likely to have a difficult reelection fight under any set of circumstances. Why would he take the risk?” asked New Jersey Democratic media consultant Brad Lawrence, who counts several of the potential candidates as clients.

In an interview in May, Christie told a reporter he hasn’t decided whether he’ll run for a second term and won’t make a final call until year’s end.

Christie adviser William Palatucci wouldn’t go there, either. “I’ll talk about 2013 when we get to 2013,” he said in an email.

Many Democrats and even some Republicans said if Christie is serious about waging a White House run in 2016, another campaign in deep-blue New Jersey doesn’t make much sense.

As a term-limited lame duck, his rivals would be less hesitant to challenge him on his policy initiatives. Any attempt to make compromises with a Democratic-dominated legislature could be used against him by would-be GOP opponents ready to outflank him on the right. And plotting a run for president means he’d need to make regular jaunts to Iowa and New Hampshire soon after being sworn in for a second gubernatorial term.

That all assumes he’d win — and despite approval ratings over the 50 percent mark, that’s no sure thing in a state where any competent Democrat is likely to begin with 45 percent of the vote.

Becoming a guest contributor on the Fox News Channel, hitting the lucrative speaking circuit or setting up a federal political action committee might be a more enticing way for the 49-year-old former U.S. attorney to stay relevant.

“There’s a building body of people saying he doesn’t want to do another five years of this grind. You can see the wear and tear on him,” said Democratic state Sen. Dick Codey, who ascended to governor after the resignation of Gov. Jim McGreevey in 2004.

The latest incident of Christie mouthing off to a critic on the New Jersey boardwalk struck Codey as more evidence his abrasive approach is wearing thin.

“I know people who like his policies saying, ‘Jesus Christ, he’s got a rotten personality.’ The more you are exposed to it personally, the more you get turned off. If Romney loses, he’d be in a better position to just run for president,” said Codey, who is keeping his name in the mix as a 2013 contender.

Yet that may just be wishful thinking by Democrats hoping to avoid what would be a punishing, no-holds-barred contest against the pugnacious Christie.

As one Democratic consultant put it, “If it’s an open seat, everybody runs. The problem is Christie is such a bully and so crass, he does intimidate people from getting in the race.”

Armed with statewide name recognition and considerable residual goodwill from his two stints as governor, Codey is seen as a formidable challenger. But in interviews, Democrats wondered if he has the fire in the belly and speculated that he’s more interested in dangling his name to stay in the conversation.

“The two people that stick out in the polls are Booker and me. He’s said he’s not running publicly,” noted Codey.

When pressed if he took Booker at his word, Codey paused for several seconds before replying, “With him … God. He said it to me in a private meeting. I wouldn’t tell you that, but he also said it in the newspaper.”

Then there’s the list of second-tier candidates, who have limited constituencies and are largely unknown outside of their counties.

State Sen. Barbara Buono has been the least coy about her intentions, enlisting President Barack Obama’s media firm AKPD Message & Media and telling POLITICO she’s considering it “seriously with eyes wide open.”

“I’m certainly not the pick of the party bosses. I’m driven by independence. I laid down my tracks as a progressive voice,” said Buono, who was ousted from leadership last year after frequent clashes with current state Senate president Stephen Sweeney, another potential gubernatorial candidate.

Other possibilities are state Democratic committee chairman John Wisniewski and Assembly Leader Lou Greenwald, who said in an interview a race against Christie would be “something I’d love to do.”

“This will almost be like a presidential race, it will be in the limelight. That’s not lost on me,” said Greenwald. “The good news is that there will only be two gubernatorial races in 2013 and I think Democrats around the country will look at this as an opportunity to put a stake in the ground.”

The Democratic Governors Association has had preliminary conversations with several prospects, but in a statement signaled they were enamored by Environmental Protection Agency chief Lisa Jackson, who served as the state’s environmental enforcer under Gov. Jon Corzine.

“The DGA would be excited if Lisa Jackson was looking to run for governor. Any time we’ve heard her name mentioned, it’s in a positive light. She’d be a fresh candidate who would bring a new perspective. We also think Gov. Codey would be a great candidate who would match up well against Gov. Christie,” said DGA executive director Colm O’Comartun, who stressed the committee does not endorse in primaries.

A spokeswoman for Jackson declined comment.

It will be difficult for any of these candidates to get far out of the starting gate without winning over a majority of the tight-fisted county party bosses that wield an outsize influence over the process.

But that’s also part of the complexity in ramping up against Christie.

In interviews, several Democrats said major players like Camden County’s George Norcross — a wealthy insurance executive who bought The Philadelphia Inquirer this spring — have played nice with Christie and don’t have a financial incentive to pick a fight.

Whether on higher education, tax breaks for a new Atlantic City casino or pension reform, many Democrats have been willing partners with Christie.

That includes Booker, whose agenda in Newark depends on funding and incentives from the governor’s office.

Yet Matzen is quick to point out that Christie has just as much of a political interest in keeping Booker close.

“Chris Christie promotes the idea that they’re friends,” he said, “because Booker is the guy that they are most concerned about.”